Webster's Encyclopedic Unabridged Dictionary defines the term "camber" as "a slightly arching, upward curve, or convexity, as of the deck of a ship".
In the transport of a web material, camber generally refers to the lateral curvature of the web material. FIG. 1 illustrates a portion of a length of web material 10 having camber relative to a longitudinal axis A of the web material. Stated alternatively, if web material 10 was laid flat in plane B, there exists a curvature about an axis normal to plane B. Camber can affect the transport of the web material in a web conveyance system or web handling system. For example, camber can affect the lateral tracking offset from a desired location. Camber can also affect the lateral stability of the web material, commonly referred to as "weave". Camber can adversely affect web conveyance to such an extreme that the web cannot be conveyed through a web handling system. Accordingly, a measure or quantification of camber could provide advantages, such as an indication of how a web would track when conveyed through a web transport system.
U.S. Pat. No. 4,528,756 relates to a system for detecting camber of a rolled material. More particularly, camber is detected by detecting the right and left outlet side lengths of the rolled material using touch rollers and the plate width of the rolled material, and then processing the detected signals to calculate the radius of curvature of the plate center line of the rolled material. Such an apparatus and method may be suitable for rolled material having a defined thickness, but is not suitable for thin, flexible web material, such as photosensitive web material.
U.S. Pat. No. 4,385,716 relates to a web controlling apparatus wherein the web may show a curvature about an axis normal to a plane. No teaching is made regarding measuring the amount of camber in the web.
Accordingly, a need exists for an apparatus and method to measure or quantify the amount of camber of a web material. Preferably such a determination would be made on-line, that is, as the web material is conveyed through a web handling system. Further, the apparatus and method should be suitable for thin, flexible web material, such as photosensitive web material.